This invention is directed to improvements to U.S. Pat. No. 5,474,342 issued Dec. 12, 1995 to Smith et al. In this patent, a door latch actuator is described which is used in association with a conventional latch/bolt or dead latch bolt assembly on a conventional door which is typically mounted on a door frame for movement between a first door position and a second door position. The door latch actuator described in Smith et al includes an actuator element disposed in proximity to the distal end of the latch bolt when the door is at a first door position wherein it is secured. A driver is associated with the actuator element, and the actuator element is movable between a first actuator position and a second actuator position. In the first actuator position, the actuator element allows the distal end of the latch/bolt to engage the latch/bolt receiver when it is extended into a latch bolt cavity in the door jam. In the second actuator position, the actuator element mechanically displaces the latch/bolt from the extended state to the retracted state causing the door to be in an unsecured condition thereby permitting movement of the door. The driver moves the actuator element to accomplish this function.
Where the conventional door latch assembly in the door is of the "dead latch" type consisting of a spring latch bolt with an associated dead latch bolt pin, an alternative door latch actuator according to U.S. Pat. No. 5,474,342 has an actuator element disposed in proximity to the distal ends of both the spring latch bolt and the dead latch bolt pin. The driver moves the actuator element between the first and second actuator positions. When in the first actuator position, the actuator element is operative to retain the dead latch bolt pin in a disabled (retracted) state while allowing the spring latch bolt to extend in the latch/bolt receiving cavity. The actuator element, when moved from the first actuator position to the second actuator position, first releases the dead latch bolt pin which moves into the enabled (extended) state and afterward attacks the distal end of the spring latch bolt to move the spring latch bolt from the extended state to the retracted state.
In U.S. Pat. No. 5,474,342, several embodiments of the door latch actuator are disclosed. In one embodiment, the actuator element is a cam which is configured to have two cam lobes respectively controlling the dead latch bolt pin and the spring latch bolt. Two independent cam elements are disclosed for construction of the actuator element, and the use of two independently acting solenoids is taught in this patent. Alteratively, an articulated actuator element is described, among other embodiments.
While the door latch actuator described in U.S. Pat. No. 5,474,342 represents a significant advance over the art of automated security latch systems, further development of an automated system has revealed additional challenges where two independent plungers are used to control the spring latch bolt and the dead latch bolt pin of the door latch assembly. Whereas the above referenced patent contemplated driving two independent plungers with two separate solenoids, it is more desirable to utilize a single motor to obtain greater force for a reasonable amount of electrical power consumption. Moreover, the use of an electrical motor achieved a more compact design necessary to permit concealed installation in typical door frames.
In addition, the Smith et al patent did not completely address a situation where a secured door might be pre-stressed prior to attempted release. It can be anticipated that, in many cases, pressure will exist on the door latch in the door opening direction at the time that the door latch actuator is operated. This pressure can come from a poorly aligned door or from an impatient person already trying to push or pull the door open before the door latch actuator has had a chance to operate. The Smith et al patent addresses such a problem by utilizing sufficient mechanical force in pushing in the latch. However, the generation of such a brute force can make the construction of the actuator cumbersome so that it does not readily fit into a door frame. Alternatively, the actuator can operate slower thus trading time for force to increase the amount of actuating force but slower operation of the door latch actuator is in itself a disadvantage.
There is, however, an entirely separate problem to merely applying such sufficient force to operate the actuator system. Because of the way in which deadlatch assemblies are manufactured, when the door is in the secured condition (that is, with the latch/bolt released into the strike hole and the dead latch bolt pin pushed in), pressure on the spring latch/bolt in the door opening direction can often bind the dead latch bolt pin so that it will not come out of the disable position. Mechanized pushing on the spring latch/bolt to release the door will only serve to increase the binding force on the unit if the dead latch bolt pin has not first successfully "popped" into the enable state.
Accordingly, it may be appreciated that a need exists for automated door latch actuator devices. There is a further need for such door latch actuator devices that can improve on the construction of existing automated systems. There is a further need for providing an automated door latch actuator which anticipates and addresses door stressed conditions. There is also a need for improved methods of controlling automated door actuating systems. The present invention is directed to resolving these needs.